Precision Optics Corp. Inc. of Gardner, Mass., has sold its custom optical thin-film product line to Optometrics Corp. of Ayer, Mass., a subsidiary of Dynasil Corp. of America. Besides the purchase price of $250,000, a three-year royalty payment agreement was reached. Both companies consider the purchase to be furthering their goals, as Precision Optics plans to concentrate on its medical visualization business while Optometrics plans to expand its line of optical filters.